Technical Field
The present invention relates to analysis and diagnostics of a device under test and, more particularly, to automated analysis of an image to locate particular components that show aberrant behavior.
Description of the Related Art
Device diagnostics, and in particular scan chain diagnostics, are used to improve the yield of a manufacturing process. Scan chains may use up to 30% of a chip's available area and, therefore, provide a statistically large sample of the chip's coverage when looking for systematic and random defects.
While tester- and software-based scan chain diagnostics have been quite successful, they nonetheless suffer from low resolution and cannot identify some kinds of failure. As to the former, in most cases a scan failure may be narrowed down to only a small group of components, rather than to a single point of failure. As to the latter, tester-based methodologies cannot identify logic equivalent gates. In many cases, several other gates are inserted along a scan chain, between, e.g., consecutive latches or flip-flops. Such gates may form, e.g., buffer repeaters or multiplexers. Therefore, even in ideal conditions, the maximum resolution achievable is limited to the latch granularity, where a first latch works and the subsequent latch does not, but cannot yield any information about where the defect is located in the patch between those two latches. In reality, the distance between two latches could be thousands of microns long, with a large number of other gates in between.
While emission-based diagnostics dramatically increases the diagnostic resolution, bringing it down to individual gates and transistors, these techniques suffer from significantly longer diagnostic times. Even if adequate setup planning has been performed in preparation of a new product, a bottleneck remains in the actual execution of data collection, which involves navigation, focusing, and emission collection.
Furthermore, due to the complexity of modern circuit layouts and the limited quality of collected emission images, it can be challenging for a human operator to interpret the information gleaned through emission diagnostics. Small differences may go undetected by the human operator and may be open to personal interpretation.